We propose to purify renal renin, and to use the pure renin for its characterization, for the preparation of specific antirenin antibodies and for the development of the direct radioimmuno-assay of renin. Numerous attempts of the purification of renal renin have experienced great difficulties. Based on our successful purification of renin-like enzymes from the mouse submaxillary gland, we have invented a specific affinity chromatographic technique for the selective concentration of renin and have devised methods to stabilize this labile enzyme. These new techniques, experience and recently available general methodology for protein isolation will be applied to the purification of renal renins. The pure renins thus obtained will be used to characterize their molecular properties and mechanism of action. On the basis of these studies specific inhibitors will be designed and the mechanism of the control of renin action will be studied. A new, simple and dependable chemical assay method for renin activity will be developed and will be used in kinetic studies. Specific antibodies to renin will be prepared for use in the identification, localization and characterization of renin. Of great practical value is its application to the development of the direct radioimmuno-assay of renin, which will considerably facilitate the investigation and diagnosis of hypertension. Pure renin and systematic information of this enzyme made available by these studies will provide a basis and stimulus for further progress in research in blood pressure regulation and hypertension as well as for a better approach to the diagnosis and treatment of hypertension.